Indium-containing wafers are widely used for photodetectors such as pin photodiodes and avalanche photodiodes, light-emitting elements such as laser diodes, and electronic devices such as field-effect transistors and bipolar transistors. In order to comprehend the semiconductor characteristics of such indium-containing wafers, evaluating characteristics of the wafers in terms of density, thickness, and crystallinity is crucial.
With regard to evaluating such characteristics, capacitance-voltage measurement (hereinafter referred to as “C-V measurement”) has been employed for evaluating carrier density in and thickness of wafers; however, the mainstream C-V measurement to date has been the SPA (semiconductor profile analyzer) method. Due to the fact that the SPA method is one in which the C-V measurement is carried out while the wafer is being etched through its surface with an electrolyte, which is a solution, as an electrode, problems with the method have been errors in the carrier density measurement, associated with fluctuations in the area of wafer contact with the electrolyte, and degradation in depth accuracy owing to etching unevenness; in addition, with the method being essentially a destructive test only spot checks can be made and thus, measuring the carrier density and thickness of those wafers that are themselves offered as manufactured articles has not been possible.
In contrast, the mercury C-V method—in which the C-V measurement is carried out by providing a mercury electrode on the episurface of the wafer to employ a mercury-metal-compound-semiconductor Schottky barrier—is free from the problems of errors in carrier density measurement and degradation in accuracy with the SPA method; moreover, there is no surface etching with the mercury C-V method, which means that with mercury that has been adhered to the wafers as an electrode having been removed, wafers whose carrier density and thickness have been measured can be offered as manufactured articles. Furthermore, an advantage with the mercury C-V method is that, in addition to the C-V measurement a current-voltage measurement (hereinafter referred to as an “I-V measurement”) can be made, making it possible to gain insight into crystallinity. Nevertheless, hazards to the human body and global environment are feared, in addition to the problem of degradation in wafer characteristics, lest mercury be extant on wafers following mercury C-V measurement.